1. Field of the Invention
The present invention relates generally to the treatment of drill cuttings generated during oil and gas well drilling operations. More particularly, the present invention relates to a method and apparatus for the removal of fluids, such as drilling mud, mud additives and contaminants, from drill cuttings. More particularly still, the present invention relates to a method and apparatus for the separation of entrained and/or adherent fluids from drill cuttings, thereby permitting recovery of such fluids as well as efficient disposal of the solid components of said drill cuttings.
2. Description of the Related Art
Drilling rigs used for the drilling of oil and gas wells typically include a supportive rig floor positioned over a well, a derrick extending vertically above said rig floor, and a traveling block which can be raised and lowered within said derrick. During drilling operations, a drill bit is generally conveyed into a well and manipulated within said well via tubular drill pipe. The drill pipe is raised and lowered within the well utilizing the drilling rig derrick.
When installing drill pipe or other tubular pipe into a well, such pipe is typically installed in a number of sections of roughly equal length called “joints”. As such pipe penetrates farther and farther into a well, additional joints of pipe must be added to the ever lengthening “string” or “drill string” in the rig derrick. Thus, a typical drill string comprises a plurality of sections or joints of pipe, each of which has an internal, longitudinally extending bore. During drilling operations, a drill bit or other desired equipment is typically attached to the lower or distal end of said drill string.
During drilling operations, a fluid known as drilling mud or drilling fluid is normally pumped down the longitudinally extending bore of the tubular drill pipe, and circulated up the annular space which is formed between the external surface of said drill pipe and the internal surface of the wellbore. The basic functions of drilling mud are: (1) to cool and lubricate the drill bit and downhole equipment during drilling operations; (2) to transport pieces of drilled-up rock and other debris from the bottom of the hole to the surface; (3) to suspend such rock and debris during periods when circulation is stopped; (4) to provide hydrostatic pressure to control encountered subsurface pressures; and (5) to seal the porous rock in the well with an impermeable filter cake.
As circulated drilling mud returns to the earth's surface and is pumped out of a well, the mud often contains pieces of broken, drilled-up rock and other solid debris known as “cuttings” or “drill cuttings”. In most cases, an effluent mud stream flowing out of a well, together with associated drill cuttings, is directed to one or more devices which are specifically designed to separate such drill cuttings from the mud. Such devices include, but are not limited to, “shale shakers,” desanders, desilters, hydrocyclones and centrifuges.
Shale shakers, which are well known in the art, are essentially screens that are used to separate drill cuttings from the drilling mud. In many cases, shale shakers utilize a series of screens arranged in tiered or flat disposition relative to each other. Further, such screens are often made to vibrate in order to increase the quality of such separation. The bulk drilling mud falls through the screens by gravity, while the predominantly solid cuttings pass over the end of the screens. Certain shale shakers are designed to filter coarse material from the drilling mud, while other shale shakers are designed to remove finer particles from the well drilling mud.
Shale shakers and other cuttings-removal equipment perform a valuable function in the overall drilling process. If drill cuttings are not removed from the effluent mud stream as such mud is circulated out of a well, said cuttings would remain in the active mud system. These drill cuttings and other debris would then be recirculated into the well. This often leads to problems, because such drilled solids can dramatically alter the characteristics and performance of the drilling mud. Further, recirculation of drill cuttings can also increase wear in mud pumps and other mechanical equipment used in the drilling process. As such, shale shakers and other similar devices are frequently necessary to efficiently separate drill cuttings from drilling mud as it is circulated out of a well.
Once drill cuttings and other debris have been separated from the bulk mud stream flowing out of a well, it is necessary to dispose of such cuttings. Unfortunately, in most instances the disposal of drill cuttings can present a number of different problems. Often, the most economical way to dispose of drill cuttings would simply be to discharge said cuttings directly into the surrounding environment. However, even though drill cuttings leaving a shale shaker or other separation device may have been separated from a well's effluent mud stream, such cuttings nonetheless typically include entrained and/or adherent mud and other fluids which could be damaging to the environment.
In order for drilling mud to accomplish its intended objectives, it is often necessary to adjust or control certain characteristics of such drilling mud. Thus, chemicals and/or other additives are often mixed into such drilling muds. Common drilling mud additives include gelling agents (e.g., colloidal solids and/or emulsified liquids), weighting materials, and other chemicals which are used to maintain mud properties within desired parameters. Further, although drilling mud has historically been water-based, improved results have been obtained using oil-based or synthetic-based muds, especially in severe drilling environments. Many of these additives, oil-based muds and synthetic-based muds can be environmentally harmful. Thus, it is often undesirable and a violation of environmental regulations to release such fluid-laden cuttings directly into the surrounding environment.
In order to avoid environmental contamination and comply with applicable governmental regulations, drill cuttings are frequently transported from a drilling rig to an off-site facility for disposal. In order to accomplish such off-site disposal, drill cuttings are generally loaded into boxes or other storage containers for transportation away from the rig. While this solution can be generally functional, it is not without significant problems.
One major problem associated with the off-site disposal of drill cuttings is increased cost. In most cases, special equipment is needed to move fluid-laden drill cuttings from a rig's shale shakers to another location on the rig where storage boxes are loaded. Such equipment is often in the form of complicated and elaborate conveyors, augers and/or vacuum units. Moreover, large numbers of storage boxes must be rented or purchased in order to accommodate such cuttings. All of this added equipment and labor increases the costs associated with the drilling process.
Another major problem associated with off-site disposal of fluids-laden drill cuttings is the use of valuable rig space. Space is at a premium on most drilling rigs, and particularly those that work in a marine environment. In most instances, cuttings disposal equipment takes up a great deal of a rig's available work area. For example, large storage boxes, which must be loaded on and off a rig, take up a significant amount of space. Similarly, equipment used to move such cuttings from a rig's shale shaker to cuttings boxes can also take up a great deal of space. This additional equipment can present logistical and/or safety problems on many rigs.
Another problem associated with off-site disposal of drill cuttings is environmental impact. Such off-site disposal of drill cuttings does not necessarily guarantee an overall reduction or elimination of environmental contamination. Cuttings boxes must be transported to a rig, loaded with cuttings, and thereafter moved to an off-site storage facility. Trucks, vessels or other pollution-emitting means of transportation must typically be employed to transport said boxes to and from the rig. As a result, the overall impact on the environment of offsite disposal can be significant.
Attempts have been made to clean drill cuttings in order to remove surface contaminants prior to discharge of such cuttings into the environment. For example, certain cuttings recovery and treatment devices utilize separate cells having low speed agitators to stir a mixture of cuttings and cleansing surfactants. The cuttings are transferred from one cell to the next where additional agitation and cleansing takes place. Thereafter, a slurry of cleansed drill cuttings and surfactant is pumped from the cells to a vibrating screen operation in which most of the surfactant is removed and recovered for later use. In some cases, a portion of the surfactant solution, which is rich in fine drill cuttings and adherent drilling fluids, is run through one or more hydrocyclone separators which discharge the fine drill cuttings in solution separated from the larger, cleansed drill cuttings.
However, attempts at washing or otherwise treating drill cuttings on location have also proven to be problematic. Frequently, existing methods of washing drill cuttings require large amounts of equipment, which can cause space problems on most drilling rigs and add to the overall expense of a drilling project. Further, such cuttings washing systems utilize surfactants or other solutions which must be disposed of or, at a minimum, kept out of the surrounding environment. Perhaps most significantly, washed drill cuttings are seldom clean enough for discharge directly into the surrounding environment.
Accordingly, the need exists for a means to separate entrained and/or adherent fluids from fluids-laden drill cuttings. Said separation means should not take up a large amount of space on a drilling rig and should be easily adaptable with existing rig equipment. In areas in which on-site disposal is allowed, such separation means should remove sufficient amounts of fluids from fluids-laden drill cuttings to permit disposal of the solid components of said cuttings directly into the surrounding environment. In situations in which cuttings are stored in boxes or other means of transportation for off-site disposal, said separation means should remove enough entrained and/or adherent fluid from said cuttings to reduce the overall volume of the materials, thereby reducing the amount and/or size of the boxes needed to transport a given amount of cuttings. Additionally, there is a need for a means of separation which provides for the recovery and reclamation of fluids separated from such drill cuttings, particularly oil-based or synthetic-based drilling fluids.
It is, therefore, an object of the present invention to provide a means of removing fluids, and particularly entrained and/or adherent fluids, from drill cuttings.
It is further an object of the present invention to provide a means for recovering a greater percentage of drilling mud and other fluids from drill cuttings than existing separation methods.
It is yet another object of the present invention to provide a means of separating fluids from drill cuttings which utilizes a relatively small amount of equipment and, therefore, has minimal space requirements.
It is yet another object of the present invention to provide a means of separating fluids from drill cuttings which can easily integrate with existing rig equipment.
It is yet another object of the invention to provide a means of removing entrained and/or adherent fluids in drill cuttings being transported for off-site disposal, thereby making such transport more economical.
It is yet another object of the present invention to provide a means of separating sufficient amounts of entrained and/or adherent fluids from fluids-laden cuttings to permit efficient disposal of the solid components of said cuttings.
It is yet another object of the present invention to provide a means of separating entrained and/or adherent fluids from fluids-laden drill cuttings which permits the efficient reclamation and/or reuse of such separated fluids.